The use of polyalpha-olefins or copolymers thereof to reduce the drag of a hydrocarbon flowing through a conduit, and hence the energy requirements for such fluid hydrocarbon transportation, is well known. These drag reducing agents or DRAs have taken various forms in the past, including slurries of ground polymer particulates. A problem generally experienced with simply grinding the polyalpha-olefins (PAOs) is that the particles will “cold flow” or stick together after a relatively short time, thus making it impossible to place the PAO in the hydrocarbon in a form that will dissolve or otherwise mix with the hydrocarbon in an efficient manner. Further, the grinding process irreversibly degrades the polymer, thereby reducing the drag reduction efficiency of the polymer.
One common solution to preventing cold flow is to coat the ground polymer particles with an anti-agglomerating agent. Cryogenic grinding of the polymers to produce the particles prior to or simultaneously with coating with an anti-agglomerating agent has also been used. However, some powdered or particulate DRA slurries require special equipment for preparation, storage and injection into a conduit to ensure that the DRA is completely dissolved in the hydrocarbon stream.
Gel or solution DRAs have also been tried in the past. However, these drag reducing gels also demand specialized injection equipment, as well as pressurized delivery systems. They are also limited to about 10% polymer as a maximum concentration in a carrier fluid due to the high solution viscosity of these DRAs. Thus, transportation costs of the DRA are considerable, since up to about 90% of the volume being transported and handled is inert material.
Further, as noted, polymeric DRAs additionally suffer from the problem that the high molecular weight polymer molecules can be irreversibly degraded (reduced in size and thus effectiveness) when subjected to conditions of high shear, such as when they pass through a pump. Additionally, some polymeric DRAs can cause undesirable changes in emulsion or fluid quality, or cause foaming problems when used to reduce the drag of multiphase liquids.
Surfactants, such as quaternary ammonium salt cationic surfactants, are known drag reducing agents in aqueous (non-hydrocarbon) systems and have the advantage over polymeric DRAs in that they do not degrade irreversibly when sheared. In contrast, flow-induced structures in surfactant solutions are reversible.
Thus, it would be desirable if a drag reducing agent could be developed which rapidly dissolves in the flowing hydrocarbon or emulsion, which could minimize or eliminate the need for special equipment for preparation and incorporation into the hydrocarbon or emulsion, and which could avoid or minimize shear degradation. It would be desirable to develop a drag reducing agent that does not cold flow and thus require the use of cryogenic grinding and/or the further addition of an anti-agglomeration additive.